"Name or service not known (SocketError)" error when runs in many threads

Question

I have made a program that parses text file and download data in parallel. When runs download method in 9 or less threads, the program doesn't have error. But when runs the method in 10 or more threads, the program throws "`initialize': getaddrinfo: Name or service not known (SocketError)" error. I tried some algorithms to run in parallel, but the same problem occurs. I put the url, which was passed to 'open' method(open-uri) when "Name or service not known" error happens, into browser and confirmed that this url is valid and received correct data.Here's partial code. ``` jobs = [] aps = [] .... #jobs are pushed into jobs[] .... max_thread = 15 loop do ary_threads = [] max_thread.times do |i| break if jobs.size == 0 job = jobs.pop ary_threads << Thread.start { begin request(job[0],job[1]).each do |ap| #in "request" method, open(url)are called aps.push(ap) end end } end ary_threads.each { |th| th.join } break if jobs.size == 0 end ``` and error is ``` /usr/lib/ruby/1.9.1/net/http.rb:76…

Accepted Answer

I think it might be because of race condition between threads. Try doing the operations atomically. Put the mutex lock.

```
    @mutex = Mutex.new

@mutex.syncronize do
      ...

ary_threads << Thread.start {
       begin
        request(job[0],job[1]).each do |ap| #in "request" method, open(url)are called
          aps.push(ap)
        end
        end
      }

...
    end
```

"Name or service not known (SocketError)" error when runs in many threads

Solution

Problem